Most patients with castrate-resistant prostate cancer will receive treatment with docetaxel, after which treatment with the combination of abiraterone and prednisone has been shown to be effective. Evidence has shown an interaction between the pathways through which BKM120 and abiraterone act on cancer. Therefore, it is thought that the treatment of castrate-resistant prostate cancer will be enhanced by combining BKM120 with abiraterone plus prednisone. The purpose of this study is to determine a safe dose for the combination of daily oral BKM120, abiraterone acetate, and prednisone in patients with castrate-resistant metastatic prostate cancer who have received prior treatment with docetaxel.